my answer too - yes you can be really accurate if you like, but I wouldnt bother buying anything unless I was running at BSB level or higher…
and in my opinion, its not the tyre that you need to worry about measuring - it’s the rims - when the tyre warmers are on, if the rim is warm to the touch, then the tyres are warm enough
Maplin sell an infra-red device which works OK, it’s calibrated for black surfaces. Seems to give a temp reading which is within a few degrees of a thermometer. Also has a laser pointer built into it . . . which to be honest is more fun than the gauge . . .
i have an infrared lazer thingy but find a much better use for it is checking exhaust temperatures when rejetting carbs …or pointing it at girls breasts, you may be surprised how hot they can get ;)